1. Field of the Disclosure
The instant disclosure relates to a receiver; in particular, to a signal demodulation module for a receiver.
2. Description of Related Art
As people should know, communication includes wire/wireless communication supported by wire/wireless communication equipment. Communication systems include domestic/international cellular telecommunication system, Internet, and point-to-point indoor wireless network. Each type of the communication systems is constructed and operated according to one or a plurality of communication standard. For example, wireless communication may be operated according to one or a plurality of standard such as Institute of Electrical and Electronics Engineers (IEEE) 802.11, Bluetooth, Advanced Mobile Phone System (AMPS), digital AMPS, Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution system (MMDS), and/or a variation version from any of the above, and it is not limited thereto.
According to a type of a wireless communication system, the wireless communication equipment directly or indirectly communicates with another wireless communication equipment. The wireless communication equipment may be: a cellular phone, a bidirectional radio transceiver, a personal digital assistant (PDA), a personal computer (PC), a laptop, a home entertainment device. As for the direct communication (also known as point-to-point communication), the wireless communication equipment which are involved in a communication modulate their receivers and transmitters on the same channel/channels, and communicate through the channel/channels. Each of the channels may be set according to one or more than one carriers from a plurality of the radio frequency carriers of the wireless communication system. As for the indirect wireless communication, each of the wireless communication equipment via a distributed channel to directly communicate with related base (such as a cellular operation system) and/or related base station (such as indoor or building wireless network). To complete a communicating connection between the wireless communication equipment, the related base and/or base station communicate with each other via a system controller, a public switched telephone network, Internet, and/or other wide area network.
To be involved in the wireless communication, each of the wireless communication equipment includes a wireless transceiver built inside (the wireless transceiver includes a receiver and a transmitter), or is coupled to a related wireless transceiver (such as an indoor work station and/or a building wireless communication network, a radio frequency modem). A regular transmitter follows a wireless communication standard of a generated base-band signal to modulate data, and transform the data into a radio frequency signal. The base-band signal is frequency-mixed in one or a plurality of IF stage and a local oscillator to generate the radio frequency signal. Regularly, a receiver includes an antenna, a filter, a low noise amplifier, an IF stage, and a demodulator. The antenna receives a radio frequency signal and provides to the filter, and the filter transmits the radio frequency signal filtered to the low noise amplifier. The low noise amplifier amplifies the radio frequency signal filtered and provides to the IF stage. The IF stage converts (reduces) the radio frequency signal amplified into a medium frequency or base-band signal. The IF stage provides an IF signal or a base-band signal to the demodulator, and the demodulator reacquires the data according to a modulation protocol.
In wireless communication, there are particular requirements for specifications regarding a carrier band width of different frequency bands, a size of a signal channel, and a data transferring rate. In comparison to a specification of a receiver for the mobile phone, design requirements of the specification of a receiver used in biomedical electronic fields are relatively lenient. However, it is quite strict when it comes to power efficiency, and with an application method of implantation, there is limited power source from the outside. Therefore, it is a current issue in how to maintain an overall low power efficiency and high energy efficiency, and to keep a specific transmission distance and amount of data needed.
In prior arts, the receiver demodulates mainly with two oscillators, and a center frequency of the two oscillators must be respectively higher and lower than a frequency of a signal injected, and thus a great input power is required for a regular operation. Furthermore, it is able to demodulate Binary Phase Shift Keying (BPSK) with the method in prior arts that is to demodulate with the two injection-locked oscillators; however, there is no absolute reference phase in the demodulation mechanism, and thus it is possible to cause a series of mistakes when a mistake happens, and thus leads to a high Bit Error Rate (BER).